Project No.1 seeks to investigate the quantitative retinal output of ganglion cells subserving color vision in the ground retina. Only one basic type of opponent-color unit (the BG-G unit) has been found, and their output response patterns demonstrate a functional capacity to code hue by temporal patterning. Exploration of this concept (the temporal theory) will be carried out by quantitative tests of response properties of BG-G units that can be correlated with the animal's behavioral responses. Project No.2 seeks to extend systems analysis (both linear and nonlinear) to continue characterizing the response properties of neurons that fire repetitively. The study will concentrate on extending observations made on the tonic stretch receptor of the crayfish and on the eccentric cell of Limulus to the phasic stretch receptor of the crayfish. Consequences due to the nonlinearity of encoder output will be examined with respect to its interaction with feedback, and its significance to information processing. BIBLIOGRAPHIC REFERENCES: Fohlmeister, J., Poppele, R., and Purple, R.L. (1975). Determination of neuronal feedback parameters from spike train analysis. Society for Neuroscience, 5th Annual Meeting, New York, p. 1021. Gur, M. and Purple, R.L. Blood-pressure responses as an indicator of anesthetic level in the ground squirrel. J. Appl. Physiol., in press, 1976.